Liquid crystal display devices are improving in performance with expansion of their applications. In particular, display modes with wide viewing angle characteristics, for example, MVA (Multi-domain Vertical Alignment) and IPS (In Plane Switching), have been developed, and are undergoing further improvements.
In recent years, liquid crystal display devices of an FFS (Fringe Field Switching) mode, which is an extended form of the IPS mode, have also been developed. In the IPS mode and the FFS mode, an electric field is generated in an in-plane direction (or an oblique direction) by using electrodes which are provided on one of the substrates between which a liquid crystal layer is interposed, and this electric field causes liquid crystal molecules to be rotated in the substrate plane to provide display. These display modes are also referred to as a lateral electric field mode (lateral electric field method).
According to a known driving method for a liquid crystal display device of a lateral electric field mode, liquid crystal molecules in each pixel are rotated uniformly such that major axes thereof are aligned in the same direction in the presence of an applied voltage. However, in the state where the liquid crystal molecules are aligned in the same direction, the difference in the refractive index between the major axis direction and the minor axis direction of a liquid crystal molecule results in a so-called color shift. This is a phenomenon that the color of display appears different when viewed from an oblique direction, as compared with when viewed from the front.
As a device that suppresses such a color shift, a liquid crystal display device of a dual domain mode, in which two domains are provided in each pixel, is known. In such a liquid crystal display device, two sub pixel regions which are different in terms of the electrode structure (specifically, the direction in which slits made in a pixel electrode extend, etc.) are provided in each pixel. In the presence of an applied voltage, liquid crystal molecules are rotated in opposite directions in the two different sub pixel regions. As a result, two liquid crystal domains are formed in correspondence with the two sub pixel regions.
In a typical liquid crystal display device of a dual domain mode, when a maximum voltage is applied, two domains are formed in which directors of liquid crystal molecules are substantially orthogonal to each other. In the state where the directors are substantially orthogonal to each other, the liquid crystal molecules are prevented from being viewed only in a specific direction thereof (e.g., direction which is parallel to the major axis direction). As a result, deviating apparent retardations are mutually compensated for, and thus a color shift is suppressed.
Patent Document 1 discloses a liquid crystal display device of an IPS mode in which a plurality of domains are formed. In this liquid crystal display device, the initial alignment direction of liquid crystal molecules is set to be 45° in all pixels, and elongated electrodes in two adjacent pixels extend in different directions from each other. For example, the elongated electrode in one pixel is set to extend in a direction parallel to gate bus lines (horizontal direction) whereas the elongated electrode in a pixel adjacent to the one pixel is set to extend in a direction parallel to source bus lines (vertical direction). When a voltage is applied to these two pixels, the directions of electric fields generated by the elongated electrodes in these two pixels are different from each other by 90°. Therefore, the liquid crystal molecules in these pixels are aligned in opposite directions to each other. Namely, in two adjacent pixels, the alignment directions of the liquid crystal molecules in the presence of an applied voltage are different from each other, which suppresses a color shift.
Patent Document 1 also discloses a structure in which the pixel electrode structure is different as described above between two pixels adjacent to each other in the horizontal direction and also between two pixels adjacent to each other in the vertical direction. Two pixels adjacent to each other in an oblique direction have the same pixel electrode structure. In such a structure, the liquid crystal molecules are rotated in the same direction in the two pixels adjacent to each other in an oblique direction. By contrast, pixels in which the liquid crystal molecules are rotated in different directions from each other are arrayed alternately in the horizontal direction and in the vertical direction.
Patent Document 2 discloses a liquid crystal display device of an IPS mode or an FFS mode in which four liquid crystal domains are formed in each pixel in the presence of an applied voltage. In this liquid crystal display device, four regions in which the directions of the electric fields are different are provided in each pixel. In two predetermined regions among the four regions, the directions of the electric fields are symmetrical with respect to the rubbing direction, and the liquid crystal molecules are rotated in opposite directions to each other. In the other two regions, the directions of the electric fields are symmetrical with respect to the rubbing direction although the angle of the directions of the electric fields with respect to the rubbing direction is different from that in the above two regions, and the liquid crystal molecules are rotated in opposite directions to each other. Namely, two types of regions each including two regions in which the liquid crystal molecules are rotated in opposite directions to each other are provided.